获取当前的UIViewController

+ (UIViewController *)getCurrentViewController {
    UIViewController *result = nil;
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    //app默认windowLevel是UIWindowLevelNormal，如果不是，找到它
    if (window.windowLevel != UIWindowLevelNormal) {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow * tmpWin in windows) {
            if (tmpWin.windowLevel == UIWindowLevelNormal) {
                window = tmpWin;
                break;
            }
        }
    }
    id nextResponder = nil;
    UIViewController *appRootVC = window.rootViewController;
    //1、通过present弹出VC，appRootVC.presentedViewController不为nil
    if (appRootVC.presentedViewController) {
        nextResponder = appRootVC.presentedViewController;
    }else{
        //2、通过navigationcontroller弹出VC
        NSLog(@"subviews == %@",[window subviews]);
        UIView *frontView = [[window subviews] objectAtIndex:0];
        nextResponder = [frontView nextResponder];
    }
    //1、tabBarController
    if ([nextResponder isKindOfClass:[UITabBarController class]]){
        UITabBarController * tabbar = (UITabBarController *)nextResponder;
        UINavigationController * nav = (UINavigationController *)tabbar.viewControllers[tabbar.selectedIndex];
        //或者 UINavigationController * nav = tabbar.selectedViewController;
        result = nav.childViewControllers.lastObject;
    }else if ([nextResponder isKindOfClass:[UINavigationController class]]){
        //2、navigationController
        UIViewController * nav = (UIViewController *)nextResponder;
        result = nav.childViewControllers.lastObject;
    }else{//3、viewControler
        result = nextResponder;
    }
    return result;
}